Efficient OLEDs utilize an organic host material doped with an organometallic phosphor optimized for light emission efficiency and color. Blocking layers are used between host and charge transport (hole or electron) layers to eliminate non-radiative processes that reduce efficiency. Development of host and blocking materials for blue phosphorescent OLEDs is particularly challenging because such materials must have a wide bandgap and high triplet exciton energy, ET >2.8 eV. We have developed organic phosphine oxide (PO) materials that exhibit good electron injection and transport properties while maintaining triplet energy ~3.0 eV. Such materials, however, show no measurable ability to inject and transport holes, making it impossible to achieve charge balance in the recombination zone. Here, we present design strategies for engineering ambipolar charge-transporting PO host materials and hole blocking materials for blue OLEDs. Ambiploar host materials were developed by combining hole-transporting moieties with PO-based electron-transporting moieties (ETm). The use of the same ETm in designing the hole blocking materials gave rise to hosts and blocking materials with improved energy matching. We used computational modeling using the NWChem package to determine three parameters: HOMO and LUMO energies and the intramolecular reorganizational energies ÉnDesign, syntheses of hosts and blocking materials be presented, along with photophysical and OLED data.